The present invention is directed to a method of and a system for determining if a base station is capable of receiving messages in automatic retransmission request (ARQ) format.
With reference to FIG. 1, it is known in the art to have a mobile station 20 in radio communication with a base station 22, which is connected to and in communication with a public switched telephone network 24. Radio communication between the mobile station 20 and the base station 22 is represented by a double-headed arrow 26.
In particular, the mobile station 20 and the base station 22 communicate on various radio frequencies, also referred to in the art as channels. The channels are usually classified as being either traffic channels or control channels. The traffic channels are used to bear information during the conversation state of a call. The control channels are used for the exchange of information between the mobile station 20 and the base station 22 relating, for example, to call setup (i.e. initiating a communications session between the mobile station 20 and the base station 22 on a traffic channel).
To send a voice or data message from the mobile station 20 to the base station 22, the mobile station 20 first sends a traffic channel (origination) request message on a control channel to the base station 22 to request access to one of the traffic channels associated therewith. In response, the base station 22 sends a traffic channel assignment message to the mobile station 20 on a control channel containing a designation of the traffic channel which is allocated to the mobile station 20. (These steps are referred to as xe2x80x9claunchingxe2x80x9d the communication). The mobile station 20 then uses the allocated traffic channel to transmit a voice or data message from the mobile station 20 to the base station 22.
It is also known in the art that there are two general types of radio communication systems, analog and digital, with control and traffic channels on an analog system being referred to as analog control and traffic channels, and with control and traffic channels on a digital system being referred to as digital control and traffic channels. The two types of systems differ in that a message on the traffic channel of a digital system is digitized, i.e. the message is divided up into small segments which are then transmitted and reassembled upon receipt to form the message.
For example, if the traffic channel is a digital traffic channel, then a message to be communicated between the mobile station 20 and the base station 22 is divided into a number of segments, referred to as frames. At the present time, the individual frames are transmitted one at a time in one of a plurality of time slots into which the traffic channel is divided in the time domain. Typically, a digital traffic channel is presently divided into three time slots.
When the base station 22 receives a message on a digital traffic channel, the base station 22 will initially wait to assemble all of the frames received from the mobile station 20, and then attempt to reconstruct the message. If one or more of the frames are lost in transmission between the mobile station 20 and the base station 22, however, the base station 22 will be unable to reconstruct the message, and the message is lost. The frames may be lost, for example, because of electromagnetic noise on the traffic channel, noise being practically impossible to absolutely filter out of all radio communications.
It is therefore known in the art to format the message to be transmitted on a digital traffic channel in what is known as automatic retransmission request (ARQ) format. In ARQ format, each of the frames of the message is given a frame number. As a consequence, the base station 22 can determine whether all of the frames of the message have been received from the mobile station 20. If one or more frames of the message are missing, i.e. have not been received by the base station 22, the base station 22 can send an ARQ status frame to the mobile station 20 asking for retransmission of those specific frames which were not received by the base station 22. In this fashion, the loss of one or more frames in the transmission of a message from the mobile station 20 to the base station 22 does not result in the loss of the entire message.
Unfortunately, not all base stations are equipped to receive messages from a mobile station in ARQ format. Consequently, it is necessary for a mobile station, such as the mobile station 20, to determine whether the base station, for example the base station 22, is ARQ capable.
It is therefore known in the art for a mobile station, such as the mobile station 20, to prepare a capability update request which is transmitted to the base station 22. The base station 22 then responds with a capability update response, from which the mobile station 20 can determine the ARQ capability of the base station 22.
This prior art method is explained in greater detail with reference to FIGS. 1 and 2. A mobile station 20 used in the prior art method described above may have an antenna 28, a transmitter/receiver 30, a microprocessor 32, a memory 34, an input/output assembly 36, and a bus 38. The bus 38 can be used to transfer information between the transmitter/receiver 30, the microprocessor 32, the memory 34, and the input/output assembly 36. In addition, the base station 22 has an antenna 39 which is used to receive messages from the mobile station 20.
As is shown in FIG. 2, upon receiving a message at a block 40, a program operating in the microprocessor 32 formats a capability update request at a block 42. The program controls the microprocessor 32 to transmit the capability update request via the transmitter/receiver 30 and the antenna 28 to the base station 22 at a block 44.
The mobile station 20 then waits for a capability update response to be sent from the base station 22 to the mobile station 20 at a block 46. Once the capability update response has been received by the mobile station 20, the program controls the microprocessor 32 to read the response and to determine therefrom whether the base station 22 is ARQ capable at a block 48.
If the base station 22 is ARQ capable, then the program controls the microprocessor 32 to format the message received at the block 40 in ARQ format at a block 50. The program then controls the microprocessor 32 to control the transmitter/receiver 30 to send the message formatted in ARQ to the base station 22 at a block 52. The program ends at a block 54.
If the microprocessor 32 determines at the block 48 that the base station 22 is not ARQ capable, then at block 56 the program controls the microprocessor 32 to format the message received at the block 40 in non-ARQ format. The microprocessor 32 then controls the transmitter/receiver 30 at a block 58 to transmit the message in non-ARQ format to the base station 22. The program then ends at the block 54.
One disadvantage of the prior art method is the time required for the mobile station 20 to format the capability update request and for the base station 22 to format the capability update response. The preparation of the request and the response can cause a delay in communication between the mobile station 20 and the base station 22 which is typically viewed by users of mobile stations 20 as undesirable.
Another disadvantage of the prior art method is that while the request typically takes only a single frame, the response usually requires two frames. As a consequence, the process of determining the ARQ capability of a base station requires three links, one uplink and two downlinks. The additional downlink required adds time to the overall method.
Alternatively, provided the communication between the mobile station 20 and the base station 22 is launched using a digital control channel, the mobile station 20 may be able to determine the ARQ capability of a base station 22 by continuously determining the protocol version that is being transmitted on the digital traffic channel used to communicate with the base station 22. From the protocol version information, and from information from the digital control channel on which the message was originally launched from the mobile station 20, it is possible for the mobile station 20 to infer whether the base station 22 which it is presently in communication with supports ARQ messages.
This method breaks down if the mobile station originally launched communication on an analog control channel, or if the mobile station 20 is handed off to an analog traffic channel at any point during the transmission. Under such circumstances, it may be nearly impossible for the mobile station 20 to determine the ARQ capability of the base station 22 based on the protocol version transmitted with a digital traffic channel.
A further alternative is to transmit all messages from the mobile station 20 in non-ARQ format if the mobile station 20 is ever handed off to an analog traffic channel, or if the transmission is initiated from an analog control channel. Such a method has the obvious disadvantage that it does not take advantage of the ARQ format in those base stations 22 which support ARQ formatted messages.
According to an aspect of the present invention, a digital radio communication system has a mobile station and a base station, the mobile station transmitting messages to the base station in a series of frames. Each frame has a header with a frame number and an optional polling indicator. A method of determining whether the base station is capable of receiving a message in automatic retransmission request (ARQ) format is provided. The method includes the step of transmitting from the mobile station to the base station a single frame in ARQ format with a polling indicator set such that the base station is prompted to send a status frame in ARQ format if the base station is capable of receiving messages in ARQ format. The method also has the step of determining if a status frame in ARQ format is sent from the base station to the mobile station in response to the single frame.
The method may also have the step of providing a message to be transmitted from the mobile station to the base station. Additionally, the method may have the step of formatting the message to be transmitted from the mobile station to the base station as at least one message frame in ARQ format, the one message frame corresponding to the single frame.
In a preferred embodiment, the step of determining if a status frame in ARQ format is sent may include the step of determining if a status frame in ARQ format is sent from the base station to the mobile station within a predetermined period of time from when the single frame was transmitted from the mobile station to the base station. The predetermined period of time may be three seconds.
According to another aspect of the invention, a digital radio communication system has a mobile station and a base station, the mobile station transmitting messages to the base station in a series of frames. Each frame has a header with a frame number and an optional polling indicator. A method of managing communication between the mobile station and the base station is provided. The method includes the step of formatting a message to be communicated from the mobile station to the base station as at least one message frame in automatic retransmission request (ARQ) format. The method also has the step of transmitting from the mobile station to the base station the one message frame in ARQ format with a polling indicator set such that the base station is prompted to send a status frame in ARQ format if the base station is capable of receiving messages in ARQ format. Additionally, the method has the step of transmitting any frames of the formatted message other than the one message frame in ARQ format only if the status frame in ARQ format is received from the base station by the mobile station.
In a preferred embodiment, the step of transmitting any frames of the formatted message other than the one message frame may include the step of transmitting any frames of the formatted message other than the one message frame in ARQ format only if the status frame in ARQ format is received from the base station by the mobile station within a predetermined time from when the one message frame was transmitted from the mobile station to the base station. The predetermined period of time may be three seconds.
The method may include the step of transmitting the message in a format other than the ARQ format if the status frame in ARQ format is not received from the base station. Moreover, the step of transmitting the message in a format other than ARQ format may include the step of transmitting the message in a format other than ARQ format if a status frame in ARQ format is not received from the base station within a predetermined period of time from when the one message frame was transmitted from the mobile station to the base station. Preferably, the predetermined period of time is three seconds.
According to a further aspect of the present invention, a mobile station capable of communicating with a base station is provided. The mobile station has a transmitter/receiver and a microprocessor coupled to the transmitter/receiver. A program operates in the microprocessor to transmit from the mobile station to a base station via the transmitter/receiver a single frame in automatic retransmission request (ARQ) format with a polling indicator set such that the base station is prompted to send a status frame in ARQ format if the base station is capable of receiving messages in ARQ format. The program also operates in the microprocessor to operate the microprocessor to determine if a status frame in ARQ format has been received by the transmitter/receiver from a base station in response to the single frame.
Moreover, the program may operate in the microprocessor to operate the microprocessor, in response to receipt of a message to be transmitted from the mobile station to the base station, to format the messages at least one message frame in ARQ format, the one message frame corresponding to the single frame.
In a preferred embodiment, the program may operate in the microprocessor to operate the microprocessor to determine if a status frame in ARQ format is sent from a base station to the mobile station within a predetermined period of time from when the single frame was transmitted from the mobile station to the base station. The predetermined period of time may be three seconds.